28 S. SAGUCHI 



and cells in small groups are enclosed by the basal membrane, 

 thus forming a part of the acinus. The cell cord of the typical 

 islet is enclosed by a delicate membrane which is either in direct 

 continuity with the basal membrane of the acinus or separates 

 the islet cells from the neighboring acinus cells; a special bound- 

 ary membrane or capsule around the islet does not exist. 



RELATION BETWEEN ISLET CELLS AND ACINUS CELLS 



Postembryonic development of islet cells 



Concerning the development of the islet, there is wide diver- 

 gence of opinion among different investigators. Gianneh ('98), 

 Diamare ('99), Opie ('00), Pearce ('02-'03), Kuster ('04), Helly 

 ('06), and others beheve that the islet, although derived from 

 the primitive undifferentiated pancreatic cell cords of the acinus 

 remains independent through life. There are many others who 

 assume that not only primitive cell cords, but also specific dif- 

 ferentiated pancreatic cells (i.e., acinus cells containing zymogen 

 granules) may give rise to islet cells. Lewaschew ('86), Pisch- 

 inger ('95), Laguesse ('95-'96, '01, '05,'09-'10),Mankowski ('02), 

 Tschassownikow ('06), Dale ('04), Vincent and Thompson ('07), 

 and Fischer ('12) are supporters of this hypothesis. The argu- 

 ments on which it is based are: 1) the absence of a boundary 

 membrane between the islet and acinus tissue and the immediate 

 contact or connection between the two; 2) the presence of tran- 

 sitional forms between them. It has been assumed by some that 

 acinus cells transform into islet cells by the gradual disappear- 

 ance of zymogen granules and by the change in shape, size, and 

 staining reactions of the cell-body and the nucleus, while the 

 lumen is lost to view and the cell boundaries become indistinct. 

 Laguesse ('01), among others, states that in the transformation 

 of acinus cells into islet cells the zymogen granules diminish in 

 number and come to stain more faintly, while the minute gran- 

 ules characteristic of the islet cells appear in the base of the cell. 

 These granules gradually increase in number so that the cell in 

 question finally assumes the appearance of a typical islet cell. 

 Tschassownikow ('06) regards the cells which contain chroma- 



